Transcript Chapter 9
Visualizing Physical Geography by Alan Strahler and Zeeya Merali Chapter 9 Volcanic and Tectonic Landforms Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Continental landforms are the result of endogenic and exogenic processes. • Endogenic process: works from within the Earth • Produces initial landforms • Uplifts; brings fresh rock to the surface • Powered by Earth’s internal energy • Exogenic process: works at Earth’s surface • Wears down initial landforms • Creates sequential landforms Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Volcanic Activity Volcano: conical, circular structure built by accumulation of lava flows and tephra (volcanic ash) Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Volcanic Activity Many volcanoes are located on subduction boundaries or rift zones. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Stratovolcanoes The nature of an eruption depends on the type of magma involved. Felsic lavas associated with stratovolcanoes • • • • Rhyolite, andesite Thick, resistant to flow Builds steep slopes around volcanic vents Tall, steep cone, with crater Stratovolcano: volcano constructed of multiple layers of lava and tephra (volcanic ash) Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Stratovolcanoes • Most active stratovolcanoes on circum-Pacific mountain belt • Associated with subduction zones • Felsic lavas produce explosive eruptions • Large amounts of gas under high pressure • Central part of volcano may explode, leaving caldera: central depression Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Stratovolcanoes Exogenic processes erode stratovolcanoes Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Shield Volcanoes Shield volcanoes are associated with mafic lava (basalt) • • • • Lava thin, not viscous Holds little gas Usually quiet eruptions Lava travels long distances, spreads out in thin layers • Shield volcanoes are rounded domes, with gentle slopes Shield Volcano: low, often large, dome-like accumulation of basalt lava flows emerging from long , radial fissures on flanks Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Shield Volcanoes Some shield volcanoes form over hotspots: stationary plumes of basaltic lava welling up from the mantle Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Shield Volcanoes The Hawaiian chain was formed by the movement of the Pacific Plate over a hotspot. • Chain of islands shows motion of the plate • Active volcanoes at the southern end • Guyots (sunken islands) at the northern end Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Shield Volcanoes Basaltic lava also erupts: • Along midocean ridges • Seafloor spreading • Many volcanic islands along mid-Atlantic Ridge • Beneath continental plates • Hotspot generates large volume of basaltic lava • Forms flood basalts Basaltic lava on Heimaey Island, Iceland, on mid-Atlantic Ridge Continental flood basalts, Columbia Plateau, U.S. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Volcanic Landforms Geothermal Energy Sources Geothermal energy is energy from the heat in the Earth Regions near hot springs and geysers have hot water that can be tapped and used to drive turbines to generate electricity. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Fold Belts Compression from tectonic activity produces folds in rock strata Anticlines: upbends Synclines: troughs Folds: corrugations of strata caused by crustal compression Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Fold Belts Folds erode to form ridge-and-valley landscape • Ridges and valleys parallel • Folds may be plunging folds Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms Fault: sharp break in rock with a slippage of the crustal block on one side with respect to the block on the other • Fault lines may extend for many kilometers • Most major faults extend down several kilometers • Fault slippage varies from 1 cm to 15 m • Four main types of faults: • Normal • Transcurrent • Reverse • Overthrust Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms Normal faults are produced by crustal extension Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms The East African Rift Valley is a graben Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms Transcurrent or Strike-slip Faults are produced when tectonic plates move past each other horizontally Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms Reverse and overthrust faults are produced by compression in the crust Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Tectonic Landforms Faults and Fault Landforms • Repeated faulting can produce high fault scarps • Landforms are modified by erosion Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Earthquakes Earthquake: a trembling or shaking of the ground produced by passing seismic waves • Most earthquakes produced by sudden slippage along faults • Energy builds up until the fault slips, releasing seismic waves • Earthquake magnitudes may be described on the Richter Scale Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Earthquakes Earthquakes usually occur on plate boundaries •Large-magnitude earthquakes are generated along subduction zones •Transcurrent faults on transform boundaries cause moderate to strong earthquakes •Spreading plate boundaries produce moderate earthquakes •Some earthquakes occur in the centers of continents, away from plate boundaries Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Earthquakes Earthquakes Along the San Andreas Fault San Francisco Earthquake, 1906 •700 lives lost •$30 billion damage • Generated by movement on San Andreas Fault • This portion of the San Andreas has not moved since 1906 Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Earthquakes Earthquakes Along the San Andreas Fault • Loma Prieta Quake, 1989 •62 lives lost •$6 billion damage •Occurred on fault near the San Andreas •Did not fully relieve strain on San Andreas • Southern California: likelihood of very large earthquake within 30 years is 50% Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Earthquakes Seismic Sea Waves Tsunami: train of sea waves triggered by an earthquake (or other seafloor disturbance) traveling over the ocean surface Banda Aceh, Indonesia, before and after 2004 tsunami Kalutara Beach, Sri Lanka, before and during 2004 tsunami Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Landforms and Rock Structure Exposed Batholiths and Monadnocks Batholiths: huge bodies of intrusive igneous rock • Form hilly or mountainous uplands • Monadnock: a mountain that rises out of a surrounding plain and that develops because it consists of more resistant rock than the bedrock of the surrounding region Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.